The present invention relates to a classifier for separating particulate matter according to size.
Classifiers are known in which net or centrifugal force is used to classify or separate particles according to size. However, such classifiers are not entirely suitable for classifying fine powders. A classifier for classifying or separating fine particulate matter such as ceramic powder is disclosed in Japanese Application No. 54-076092. The operation of this classifier is illustrated in FIG. 1 herein. Two clean (particle-free) air flows surround a gas flow which contains particles to be separated or classified by the so-called impact phenomenon. As illustrated in FIG. 1, the gas stream containing the particles flows into the classifier through inlet 1, while the two clean air streams flow into the classifier through inlets 2 and 3 resulting in a three-phase stream of circular cross-section within the classifier. This three-phase flowing stream reaches nozzle 4 which has a circular cross-section, where finer particles are separated from coarser particles and flow out with fluid passing through circular slit 5 extending around the nozzle 4 and through outlet 8. The coarser particles flow through nozzle 6 and out through outlet 7. In this instance, classification of particles is extremely sharp, i.e. there are relatively few of the coarser particles entrained with the finer particles. Therefore, the classifier of Japanese Application No. 54-076092 is suitable for fine powder classification. However, this prior art classifier is not desirable from the standpoint of energy efficiency, because the overall quantity of production is relatively low while a great deal of gas is used for classification purposes.